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Plasmonic Metamaterials for Active and Passive Light Control /


Fundamental study on plasmonics excites surface plasmons opening possibility for stronger light-matter interaction at nanoscales and optical frequencies. On the other hand, metamaterials, known as artificial materials built with designable subwavelength units, offer unprecedented new material properties not existing in nature. By combining unique advantages in these two areas, plasmonic metamaterials gain tremendous momentum for fundamental research interest and potential practical applications through the active and passive interaction with and control of light. This thesis is focused on the theoretical and experimental study of plasmonic metamaterials with tunable plasmonic properties, and their applications in controlling spontaneous emission process of quantum emitters, and manipulating light propagation, scattering and absorption. To break the limitation of surface plasmon properties by existing metal materials, composite- and multilayer-based metamaterials are investigated and their tunable plasmonic properties are demonstrated. Nanopatterned multilayer metamaterials with hyperbolic dispersion relations are further utilized to enhance spontaneous emission rates of molecules at desired frequencies with improved far-field radiative power through the Purcell effect. Theoretical calculations and experimental lifetime characterizations show the tunable broadband Purcell enhancement of 76 fold on the hyperbolic metamaterials that better aligns with spontaneous emission spectra and the emission intensity improvement of 80 fold achieved by the out-coupling effect of nanopatterns. This concept is later applied to quantum-well light emitting devices for improving the light efficiency and modulation speed at blue and green wavelengths. On the passive light manipulation, in contrast to strong plasmonic scattering from metal patterns, anomalously weak scattering by patterns in multilayer hyperbolic metamaterials is observed and experimentally demonstrated to be insensitive to pattern sizes, shapes and incident angles, and has potential applications in scattering cross-section engineering, optical encryption, low-observable conductive probes and opto-electric devices. Lastly, the concept of metamaterials is also extended to selective control of light absorption and reflection for potential solar energy applications. A high-performance spectrally selective coating based on multi-scaled metamaterials is designed and fabricated with 90-95% solar absorptivity and <30% infrared emissivity near the peak of 500 degree C black body radiation, which can be utilized for designing solar absorbers with high thermal efficiency for future high temperature concentrating solar power systems

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